JP4014006B2 - Pressure sensor - Google Patents

Description

  The present invention relates to a pressure sensor having a diaphragm structure that detects, for example, a capacitance corresponding to a pressure to be measured as a pressure, and more particularly to a pressure sensor suitable for measuring a pressure close to a vacuum.

  Conventionally, a pressure sensor having a diaphragm structure that detects a change in pressure to be measured as a change in capacitance is widely known. As an example of such a pressure sensor, a movable plate is joined to the vacuum chamber side of the diaphragm and in the vicinity of the strain-generating region, and a movable electrode and a fixed electrode are formed on opposite surfaces of the outer peripheral portion of the movable plate and the fixed portion of the diaphragm, respectively. There is a pressure sensor that detects a change in capacitance between the electrodes as a change in pressure (see, for example, Patent Document 1).

  In order to firmly support the sensor chip on the package, the sensor chip is supported on the metal frame of the package via the metal plate, the cover plate, and the buffer member, and the cover plate is supported by the metal plate and the base. A pressure sensor having a structure sandwiched and restrained is also considered.

JP 2002-267559 (page 7, FIG. 2)

  On the other hand, there is a specific problem to be solved when fixing a pressure sensor element (sensor chip) to a package, particularly in a high-accuracy pressure sensor that measures a minute pressure such as a vacuum gauge. Specifically, since the pressure sensor itself is highly accurate, the thermal stress caused by the temperature change of the package and the fixing material is transmitted to the sensor element fixed to the package, and the sensor element detects it. This is a problem that a measurement error occurs.

  In order to solve such a problem, a measure may be considered in which the package and the pressure sensor element are separated from each other, and a material whose linear expansion coefficient is an intermediate value between them is sandwiched, thereby relaxing the stress. However, since these components are joined together in a stacked state, the stress is transmitted between the rigid bodies because of the structure, and even if the influence of thermal stress can be alleviated to a certain extent, the micro pressure measurement At this time, measurement error is caused by the influence of the thermal stress.

  In particular, when a pressure sensor for fine pressure measurement is used in a semiconductor manufacturing process, the pressure of a high-temperature process gas close to vacuum must be measured. Therefore, the problem of the action of thermal stress due to the difference in coefficient of thermal expansion between the pressure sensor package and each component housed in the package cannot be solved.

  On the other hand, in order to alleviate the influence of such thermal stress, a measure to make the sensor element and the package considerably separated can be considered. Specifically, there is a structure in which a pedestal such as Pyrex (registered trademark) glass is provided in the package, and the sensor chip is arranged on the upper surface of the pedestal at a certain distance from the package. However, in such a structure, the entire pressure sensor is increased in size, which is against the demand for downsizing the pressure sensor itself.

  An object of the present invention is to provide a pressure sensor that is hardly affected by thermal stress due to heat from the outside and can always perform highly accurate pressure detection.

In order to solve the above-described problems, a pressure sensor according to the present invention includes a sensor chip that detects pressure, a pedestal plate that supports the sensor chip, and a support diaphragm that is joined to the pedestal plate and supports the pedestal plate. a part of the support diaphragm is joined to the package, the support diaphragm only through the sensor chip, the base plate is supported in the package, the first base plate and the second pedestal plate made of the same material The support diaphragm is joined in a state of being sandwiched between the first pedestal plate and the second pedestal plate.

In the internal space of the package, the sensor chip and the pedestal plate are supported only via a support diaphragm so as not to directly contact the inner wall of the package. As a result, the thermal stress caused by the rapid thermal change acting on the pressure sensor itself can be relaxed with the flexibility of the support diaphragm against the thermal stress. As a result, measurement accuracy is unlikely to deteriorate due to the influence of heat applied to the pressure sensor.
Further, by joining the support diaphragm and the pedestal plate in a so-called sandwich shape, the generation of thermal stress due to the bimetal effect is alleviated, and the influence of heat applied to the pressure sensor is removed, thereby making it difficult to reduce the measurement accuracy.

The pressure sensor according to claim 2 of the present invention is the pressure sensor according to claim 1, wherein the sensor chip is provided with a contact pad electrically connected to the electrode portion of the sensor chip, and the package is provided with the package. An electrode lead is provided, and the contact pad and the electrode lead are electrically connected to each other by an elastic body having flexibility for protecting the sensor chip.

  Even if the support diaphragm is displaced by thermal stress due to the difference in linear expansion coefficient between the package and the support diaphragm, or when the pressure applied to the pressure sensor suddenly rises, conduction between the electrode lead and the contact pad The elastic body having sufficient properties is sufficiently bent and does not apply excessive stress to the sensor chip, so that the measurement accuracy is not adversely affected.

  According to the pressure sensor of the present invention, it is possible to obtain a pressure sensor that is hardly affected by thermal stress due to heat from the outside and can always perform highly accurate pressure detection.

  Hereinafter, a pressure sensor according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a pressure sensor 1 according to an embodiment of the present invention includes a package 10, a pedestal plate 20 accommodated in the package, and a sensor chip that is also accommodated in the package and joined to the pedestal plate 20. 30 and an electrode lead portion 40 which is directly attached to the package 10 and electrically connects the inside and outside of the package. The pedestal plate 20 is spaced from the package 10 and is supported by the package 10 only through the support diaphragm 50.

  The package 10 includes a lower housing 11, an upper housing 12, and a cover 13. The lower housing 11, the upper housing 12, and the cover 13 are made of Inconel, which is a corrosion-resistant metal, and are joined by welding.

  The lower housing 11 has a shape in which cylindrical bodies having different diameters are connected, the large-diameter portion 11a has a joint portion with the support diaphragm 50, and the small-diameter portion 11b has a pressure introducing portion 10A into which a fluid to be measured flows. There is no. In addition, a baffle 11c is formed at a joint portion between the large diameter portion 11a and the small diameter portion 11b, and pressure introduction holes 11d are formed around the baffle 11c at predetermined intervals in the circumferential direction.

  The baffle 11c serves to bypass the measured fluid such as the process gas from the pressure introduction unit 10A without directly reaching the sensor chip 30 described later, and causes the sensor chip 30 to include a component of the process gas and the process gas. Impurities are prevented from being deposited.

  The upper housing 12 has a substantially cylindrical shape, and is a vacuum reference vacuum chamber 10B that is independent of a region where process gas is introduced into the package via a cover 13, a support diaphragm 50, a pedestal plate 20, and a sensor chip 30, which will be described later. Is forming. Note that a gas adsorbing material called a getter (not shown) is provided in the sealed space B, and the degree of vacuum is maintained.

  Further, a stopper 12a is projected and formed at an appropriate position in the circumferential direction on the support diaphragm mounting side of the upper housing 12. The stopper 12a plays a role of restricting the pedestal plate 20 from excessively changing due to a sudden increase in pressure of the fluid to be measured.

  Further, the cover 13 is made of a circular plate, and an electrode lead insertion hole 13a is formed at a predetermined position of the cover 13, and the electrode lead portion 40 is embedded through a hermetic seal 60, and the sealing performance of this portion is ensured. Has been.

  On the other hand, the support diaphragm 50 is made of an Inconel thin plate having an outer shape matched to the shape of the casing 10, and the peripheral edge is sandwiched between the edges of the upper housing 11 and the lower housing 12 and joined by welding or the like. . The thickness of the support diaphragm 50 is, for example, several tens of microns in the case of the present embodiment, and is sufficiently thinner than the pedestal plates 21 and 22. Further, a pressure introduction hole 50 a for guiding pressure to the sensor chip 30 is formed in the central portion of the support diaphragm 50.

  On both surfaces of the support diaphragm 50, a thin ring-shaped lower pedestal plate made of sapphire, which is a single crystal of aluminum oxide, is located at a certain distance from the joint between the support diaphragm 50 and the casing 10 in the entire circumferential direction (first A base plate 21 and an upper base plate (second base plate) 22 are joined.

  Each pedestal plate 21, 22 is sufficiently thick as described above with respect to the thickness of the support diaphragm 50, and has a structure in which the support diaphragm 50 is sandwiched between both pedestal plates 21, 22. ing. This prevents this portion from warping due to thermal stress generated by the difference in thermal expansion coefficient between the support diaphragm 50 and the base plate 20.

  In addition, the upper base plate 22 is bonded to an aluminum oxide base in which a rectangular sensor chip 30 made of sapphire, which is a single crystal of aluminum oxide, is changed to the same material as the spacer 31 and the upper base plate 22 after bonding. It is joined via a material. This joining method is described in detail in Japanese Patent Application Laid-Open No. 2002-111011. The sensor chip 30 has a size of 1 cm square or less in a top view, a spacer 31 made of a rectangular thin plate, a sensor diaphragm 32 that is bonded to the spacer 31 and generates a strain in response to application of pressure, and a sensor diaphragm. The sensor pedestal 33 is formed so as to form a vacuum capacity chamber (reference chamber) 30A. The vacuum capacity chamber 30 </ b> A and the reference vacuum chamber 10 </ b> B maintain the same degree of vacuum through communication holes (not shown) drilled at appropriate positions on the sensor base 33.

  The spacer 31, the sensor diaphragm 32, and the sensor pedestal 33 are joined together by so-called direct joining to constitute an integrated sensor chip 30.

  Further, in the capacity chamber 30A of the sensor chip 30, fixed electrodes 33b and 33c made of a conductor such as gold or platinum are formed in the recess 33a of the sensor pedestal 33, and the surface of the sensor diaphragm 32 facing this is formed. The movable electrodes 32b and 32c made of a conductor such as gold or platinum are formed on the top. Further, contact pads 35 and 36 made of gold or platinum are formed on the upper surface of the sensor chip 30, and the fixed electrodes 33b and 33c and the movable electrodes 32b and 32c are connected to the contact pads 35 and 36 by wiring (not shown). Yes.

  On the other hand, the electrode lead portion 40 includes an electrode lead pin 41 and a metal shield 42. The electrode lead pin 41 is embedded in the metal shield 42 with a hermetic seal 43 made of an insulating material such as glass, An airtight state is maintained between both end portions of the lead pin 41. One end of the electrode lead pin 41 is exposed to the outside of the package 10, and the output of the pressure sensor 1 is transmitted to an external signal processing unit through a wiring (not shown). A hermetic seal 60 is interposed between the shield 42 and the cover 13 as described above. Further, conductive contact springs 45 and 46 are connected to the other end of the electrode lead pin 41.

  The contact springs 45 and 46 are urged by the contact springs 45 and 46 even if the support diaphragm 50 slightly changes due to a sudden increase in pressure caused by a sudden flow of measured fluid such as process gas from the pressure introducing portion 10A. However, it has sufficient softness not to affect the measurement accuracy of the sensor chip 30.

  Next, the operation of the pressure sensor 1 having such a configuration will be described. In the present embodiment, the pressure sensor 1 is attached to an appropriate location of a semiconductor manufacturing apparatus, for example, and a micro pressure close to a process gas vacuum (hereinafter referred to as “a process gas vacuum” during a semiconductor manufacturing process such as CVD (Chemical Vapor Deposition)). Measure “low pressure”). Hereinafter, a method for measuring the fine pressure of the process gas will be described.

  The process gas flows into the package from the pressure introduction portion 10A of the pressure sensor 1 through the pressure introduction hole 11d. At this time, even if the process gas suddenly flows in, the process gas bypasses the baffle 11c and the pressure introducing hole 11d and flows into the package, so that the process gas does not directly hit the sensor diaphragm 32. Therefore, redeposition of the components of the process gas and impurities contained in the process gas can be prevented in the sensor diaphragm 32.

  Even if the process gas is at a low pressure, the sensor chamber 32 is bent due to the vacuum in the capacity chamber of the sensor chip 30, and the distance between the fixed electrodes 33b and 33c and the movable electrodes 32b and 32c of the sensor chip 30 changes. To do. As a result, the capacitance value of the capacitor formed by the fixed electrodes 33b and 33c and the movable electrodes 32b and 32c changes. By taking out the change in the capacitance value to the outside of the pressure sensor 1 by the electrode lead part 40, the fine pressure of the process gas can be measured.

  On the other hand, in the present embodiment, the pressure sensor 1 is installed in the semiconductor manufacturing process, and the process gas is at a high temperature. Therefore, the pressure sensor 1 is attached before and after the process gas flows into the semiconductor manufacturing apparatus. A large thermal change occurs in the area. Further, since the sensor itself is heated and used, a thermal change occurs.

  Here, since the package 10 is made of metal and the pedestal plate 20 and the sensor chip 30 are made of sapphire, the coefficients of thermal expansion between these members are different. Therefore, when the package and the pedestal plate are in surface contact as in the past, the difference in thermal expansion of each member acts as thermal stress through this contact area, and this thermal stress is a sensor chip provided on the pedestal plate. It has an adverse effect on high-precision micro-pressure measurement.

  However, in the case of the pressure sensor 1 according to the present embodiment, the pedestal plate 20 and the package 10 are supported only through the thin support diaphragm 50, and the pedestal plate 20 and the package 10 are not in direct contact. Therefore, even if the degree of thermal expansion due to the difference in material between the pedestal plate 20 and the package 10 as described above is different, the thin support diaphragm 50 extends in the region sandwiched between the package 10 and the pedestal plate 20. By bending or deforming, it is difficult to transmit thermal stress to the joint between the base plate 20 and the sensor chip 30. Therefore, even if an abrupt thermal change occurs in the pressure sensor 1, thermal stress due to this thermal change is unlikely to occur in the sensor chip 30.

  Further, the pedestal plate 20 is thick, and the support diaphragm 50 is sufficiently thinner than the pedestal plate 20. Further, the support diaphragm 50 is sandwiched between the lower pedestal plate 21 and the upper pedestal plate 22 in a sandwich structure. Thus, even if there is a difference in the coefficient of thermal expansion between the members, such as a base plate 20 made of sapphire and a support diaphragm 50 made of stainless steel, for example, they do not warp like a so-called bimetal. . Therefore, the generation of thermal stress that adversely affects the sensor chip 30 can be suppressed even in this portion.

  Furthermore, contact pads 35 and 36 are formed on the sensor chip 30, and contact springs 45 and 46 having sufficient flexibility are in conductive contact with the contact pads 35 and 36. The flexibility of the contact springs 45 and 46 is such that even if the support diaphragm 50 is deformed due to a rapid pressure rise of the process gas or a thermal change of the entire pressure sensor, the sensor chip 30 moves slightly in the package. The biasing force of the contact springs 45 and 46 is sufficiently soft so as not to affect the detection sensitivity of the sensor chip 30. Therefore, the contact springs 45 and 46 do not adversely affect the pressure detection of the sensor chip 30 due to a rapid thermal change of the pressure sensor 1.

  In the above-described embodiment, the package 10 or the support diaphragm 50 is made of Inconel, but is not necessarily limited thereto, and may be made of a corrosion-resistant metal such as stainless steel or Kovar.

  The base plate 20 and the sensor chip 30 are made of sapphire, but are not necessarily limited to this material, and may be made of silicon, alumina, silicon carbide, quartz, or the like.

  Further, the connection part between the contact pads 35 and 36 and the electrode lead part 40 is configured in the form of so-called contact springs 45 and 46, but is not necessarily limited to this as long as it has sufficient flexibility as described above. It may be a form like a leaf spring. Furthermore, the electrode lead 40 and the contact pads 35 and 36 may be connected by a sufficiently soft conductive wire.

  Although it is not always necessary to provide the baffle 11c in the pressure introducing portion 10A as in this embodiment, gas components and impurities are prevented from accumulating on the sensor diaphragm 32 due to a rapid inflow of process gas. It is most effective to provide a baffle 11c.

  In addition, it is not always necessary to sandwich the support diaphragm 50 between the lower pedestal plate 21 and the upper pedestal plate 22 as in the present embodiment. That is, if the thickness of the support diaphragm 50 is made sufficiently thin relative to the thickness of the pedestal plates 21 and 22, for example, even if the pedestal plate is joined only to one surface of the support diaphragm 50, the pressure sensor 1 is heated rapidly. Even if a change occurs, it does not warp like a so-called bimetal, and it is difficult to generate thermal stress that affects the detection characteristics of the sensor chip 30.

  However, as in this embodiment, a so-called sandwich structure in which both sides of the support diaphragm 50 are sandwiched between the pedestal plates 21 and 22 makes the two pedestal plates 21 and 22 symmetrical with each other via the support diaphragm 50. To the support diagram 50, thereby suppressing the warpage caused by the thermal stress generated in the support diaphragm 50 and each of the pedestal plates 21 and 22, and generating more thermal stress due to the difference in the thermal expansion coefficient between the support diaphragm 50 and the pedestal plate 20 It can be effectively prevented.

  In fact, the inventor found that the residual stress at this joint is further reduced when the pedestal plate is joined to both sides of the support diaphragm than when the pedestal plate is joined to only one side of the support diaphragm. It was confirmed.

  Although the above-described embodiment has been described with respect to the case where a capacitive sensor chip is used, a pressure sensor including a piezoresistive sensor chip made of silicon, for example, instead of this sensor chip, By having the above-described configuration, it is possible to effectively prevent the thermal stress generated when heat is applied to the pressure sensor from being transmitted to the sensor chip, thereby enabling highly accurate pressure measurement.

  Moreover, it cannot be overemphasized that the shape of the sensor chip 30, the base plate 20, the electrode lead part 40, and the casing 10 is not limited to the above-mentioned embodiment.

  As described above, in the pressure sensor 1 according to the present invention, the pedestal plate 20 provided with the sensor chip 30 and the package 10 are connected only by the thin support diaphragm 50. That is, in the space of the package 10, the sensor chip 30 and the pedestal plate 20 are supported in the package only through the support diaphragm 50 so as not to directly contact the inner wall of the package 10. Thereby, the thermal stress caused by the rapid thermal change applied to the pressure sensor itself can be relaxed by the flexibility of the support diaphragm 50 with respect to the thermal stress. At that time, the support diaphragm 50 and the base plate 20 are joined in a so-called sandwich shape to further alleviate the generation of thermal stress due to the bimetal effect.

  Further, the package 10 is provided with electrodes, contact pads 35 and 36 electrically connected from the electrodes are formed on the upper surface of the sensor chip, and the electrode lead portion 40 and the contact pads 35 and 36 have sufficient flexibility. The contact springs 45 and 46 are in conductive contact. Thus, even if thermal stress is generated due to the difference in thermal expansion coefficient between the package 10 and the support diaphragm 50, the portion does not adversely affect the sensor chip 30 based on the generation.

  On the other hand, when the pressure sensor 1 is used as a vacuum gauge, there is a problem that contamination particles from the measurement atmosphere and gas components in the measurement atmosphere adhere to the sensor diaphragm, adversely affect the deflection of the sensor diaphragm and cause an error. However, in the pressure sensor 1 according to the present invention, such contaminants and gas components are scattered to the support diaphragm side by the baffle 11c, and therefore, due to deposition of gas components on the sensor chip 30 and adhesion of contaminants. An adverse effect on pressure measurement can be reduced.

It is sectional drawing of the pressure sensor concerning one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressure sensor 10 Package 10A Pressure introduction part 10B Reference | standard vacuum chamber 11 Lower housing 11a Large diameter part 11b Small diameter part 11c Baffle 11d Pressure introduction hole 12 Upper housing 12a Stopper 13 Cover 13a Electrode lead insertion hole 20 Base plate 21 Lower base plate 22 Upper Base plate 30 Sensor chip 30A Capacity chamber 31 Spacer 32 Sensor diaphragm 32b, 32c Movable electrode 33 Sensor base 33b, 33c Fixed electrode 35, 36 Contact pad 40 Electrode lead part 41 Electrode lead pin 42 Shield 43 Hermetic seal 45, 46 Contact spring 50 Support Diaphragm 50a Pressure introduction hole 60 Hermetic seal

Claims (2)

A sensor chip that detects pressure; a pedestal plate that supports the sensor chip; and a support diaphragm that is bonded to the pedestal plate and supports the pedestal plate, and a part of the support diaphragm is bonded to the package; The sensor chip and the pedestal plate are supported in the package only through the support diaphragm ,
The pedestal plate includes a first pedestal plate and a second pedestal plate made of the same material, and the support diaphragm is joined in a state of being sandwiched between the first pedestal plate and the second pedestal plate. pressure sensor characterized. The sensor chip is provided with a contact pad that is electrically connected to the electrode portion of the sensor chip, and the package is provided with an electrode lead, and the contact pad and the electrode lead have flexibility for protecting the sensor chip. The pressure sensor according to claim 1, wherein the pressure sensor is brought into conductive contact with an elastic body .

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